Abstract
Abstract The high-grade crystalline basement of Sri Lanka can be subdivided into three provinces distinguished by distinct isotopic model ages. This confirms the conclusions of Milisenda et al. (1988) made on the basis of much more limited data. High-grade ortho- and paragneisses from the Highland Complex in central Sri Lanka yield Palaeoproterozoic to Archaean Nd model ages from 2.0 to 3.4 Ga and reflect an extended premetamorphic crustal history. The Wanni Complex in the western and northwestern part of the island is characterized by Meso- to Neoproterozoic Nd model ages ranging from 1.0 to 2.0 Ga. The Vijayan Complex in the southeast is occupied by Neoproterozoic I-type granitoids with Nd model ages from 1.0 to 1.8 Ga. This distinct crustal province appears to fit best a detached continental margin plutonic terrane. The isotopic data preclude a common premetamorphic history of the Wanni and Vijayan Complexes with the ancient Highland Complex. The combined Nd-, Sr- and Pb-isotope data together with recent geochronological studies strongly suggest that the distinct crustal age provinces are separated by tectonic discontinuities and that they represent terranes that were accreted just prior to the high-grade metamorphic event in Neoproterozoic time.
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